1. Field of the Invention
The present invention is related to a kind of two-speed gearbox, particularly indicated to possess a simple structure to resolve the heat efficiency loss problem due to the temperature rise when it is in direct transmission.
As shown in FIG. 1, the traditional planetary two-speed gearbox makes use of the action of controlling the internal gear to attain the object of two-speed shift. In the planetary gear train with sun gear as the input shaft and planetary gear frame as the output shaft, the transmission is the one with the ratio of speed reduction equaling 1 when the internal gear rotates synchronously with the planetary gear frame. The gear shift is actually making use of the on-and-off motion of the splines. The inventor found this kind of on-and-off motion to be very smooth and applicable for use as a motion mode to improve the gearbox.
The control of temperature rise is the principal task on the demand of high speed performance. The temperature of the speed reducer should not be over 30 degrees. Otherwise, fans should he used to enhance the circulation as well as the heat dissipation. Even a cooling circulation system should be used, but often the additional cost exceeds the cost of the speed reducer itself. The way to improve a two-speed gearbox is to design a mechanism that can lower the heat efficiency loss. According to a testing for a traditional planetary two-speed gearbox performing an idling rotation, it is found that the efficiency loss resulted from the high speed is much greater than that of the two-speed precision gear (by 2-3%). At high gear, direct transmission with a ratio of 1:1, the usage occasion tends to be at high speed of 8000-2000 RPM, and the temperature rise is very high, disregarding the magnitude of the loading. At the low gear with a reduction ratio of 4:1, the usage occasion tends to be at low speed, the temperature rise is rather low at the idling rotation, and the idling temperature is stably ups and downs depending upon the magnitude of the loading. Referring to Table 1, for the same speed (6300 RPM), the temperature rise, when it is gearing down, is less than one half of the temperature rise when it is in direct transmission. Inasmuch, the high temperature rise at the ratio 1:1 is mainly due to the oil stirring. The oil stirring loss depends on the width and surface velocity of the stirrer. As shown in FIG. 1, the outside diameter of the stirrer is that of the internal gear. The stirring velocity is proportional to the outside diameter, thereby, the internal gear rotation with large outside diameter is unfavorable to the design of temperature rise.
TABLE 1 ______________________________________ The results of performing an efficiency analysis of the prior art's product ______________________________________ Speed (RPM) 6,300 6,300 1,500 1,500 Shift 1:1 4:1 1:1 4:1 Idle Temp. Rise 50.degree. C. 23.degree. C. 19.degree. C. 9.degree. C. Idle Loss 0.2 HP 0.09 HP 0.075 HP 0.034 HP Loss Efficiency (5 HP) 4% 1.8% 1.5% 0.068% Loss Efficiency (10 HP) 2% 0.9% 0.75% 0.34% ______________________________________ Note 1: In general, in direct transmission with a ratio of 1:1, one tends to use at speed 8,000.about.9,000 RPM. At the gearing down, one tends to use at low speed. As shown in Table 1, the efficiency loss (which is independent of loading) that resulted from the prior art's product at high speed operation is far greater than 3% (under rated loading), while the efficiency loss of the general gear and bearing is within 3% under the present loading. Inasmuch, the prior art's product is very unfavorable at high speed operation. Note 2: To calculate the heat dissipation according to the temperature rise, the formula is as follows: WF = .DELTA.T * 35 * A Where WF = heat dissipation (ftlb/min.) .DELTA.T = temperature rise (.degree.F.) A = heat dissipation area (sg. ft) (the heat dissipation area exposed to the air is counted as 2 sg. ft)
The stirring loss, under the conditions with the same width and speed, is proportional to the outside diameter of the stirrer. One can attain the object of lowering the stirring loss by reducing the outside diameter of the stirrer.
(The stirring loss of traditional direct transmission): (The stirring loss of present invention's direct transmission)=4:1
* The outside diameter of the traditional stirrer is at the internal gear. PA1 * The outside diameter of the present invention's stirrer is at the spline shaft.